1. Field
The presently disclosed subject matter relates to half mirrors, methods for manufacturing the half mirrors and lighting units using the half mirror, and more particularly to the half mirrors having a high durability such as a thermal resistance and the like, which can be manufactured by a simple manufacturing method. Thus, the lighting unit using the half mirror can maintain a stable reflectivity for a long term, and also can maintain a good appearance for a long-term use because the half mirror can prevent cracking therein even under tough circumstances.
2. Description of the Related Art
Half mirrors have been used as a light-emitting surface not only for vehicle lamps incorporated into vehicles, motorcycles and the like but also for lighting apparatuses such as wall washers, room lights, outdoor luminaires, etc. For example, a conventional lighting apparatus using a half mirror is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP 2007-87,629). FIG. 8a is a schematic cross-sectional view depicting a conventional lighting apparatus using a half mirror and FIG. 8b is a partial cross-sectional view depicting the half mirror shown in FIG. 8a, which are disclosed in Patent Document No. 1.
The conventional lighting apparatus 50 includes: a reflector 51 having an opening and an inner surface used as a reflective surface; a socket 52 having an electric supply line 52A attached to the reflector 51; a light source 53 attached to the socket 52 and facing the opening of the reflector 51; a transparent cover 54 having an outer surface facing the light source 53 and attached to the opening of the reflector 51; and a transparent metallic layer 55 formed on the outer surface of the transparent cover. Patent Document 1 discloses that the transparent metallic layer 55 is one of materials such as silver (Ag), aluminum (Al), molybdenum (Mo), Titanium (Ti), tantalum (Ta), platinum (Pt), palladium (Pd), gold (Au), chromium (Cr) and alloy made by the above materials, and a multi-layer interference layer made from high and low refractive index materials.
A conventional vehicle lamp using a half mirror is also disclosed in Patent Document No. 2 (Japanese Patent Application Laid Open JP 2003-115,206). The conventional vehicle lamp is provide the half mirror having a uniform thickness on a large lens, which is curved in three-dimensional directions. The conventional vehicle lamp includes an inner lens and an outer lens, which may be used as the half mirror made by a sputtering.
When the above-described half mirrors are manufactured, for example, by coating chromium on the lens using sputtering method, and when the half mirrors are heat-shocked such as repeating a low temperature and a high temperature, small cracks may occur in the half mirrors. Accordingly, the conventional half mirrors may not maintain a stable reflectivity for a long term, and also may not maintain a good appearance for a long-term use because the cracks may be caused under tough circumstances. Additionally, when the light source includes a laser device emitting light having a high emitting-intensity, the light having the high emitting-intensity may degrade qualities of the half mirrors.
The above-referenced Patent Documents and additional Documents are listed below and are hereby incorporated with their English abstracts and specification in their entireties.
1. Patent Document No. 1: Japanese Patent Application Laid Open JP 2007-87629
2. Patent Document No. 2: Japanese Patent Application Laid Open JP 2003-115206
3. Patent Document No. 3: U.S. Patent Publication No. 2016-0268770
4. Patent Document No. 4: U.S. Patent Publication No. 2016-0027968
The disclosed subject matter has been devised to consider the above and other problems, characteristics and features. Thus, exemplary embodiments of the disclosed subject matter can include half mirrors having a high durability such as a thermal resistance, which can prevent the half mirrors from cracking even under various tough circumstances such that repeat a low temperature and a high temperature. Additionally, exemplary embodiments of the disclosed subject matter can include methods for manufacturing the half mirrors having a high reliability in simple manufacturing processes.